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FIGURE 22-8 Effects of simulated altitude (549; 4,206; and 4,725 m [1,800; 13,800; and 15,500 ft]) and time of exposure on number correct for the number comparison task at two time points. Asterisks indicate a significant difference (*, P < 0.05; **, P < 0.01) from 549 m (1,800 ft). SOURCE: Lieberman et al. (1991), used with permission.

sleepiness and dizziness as well as decreased friendliness. Again, the changes observed were a function of both exposure duration and altitude level. A more detailed discussion of these results can be found in Shukitt-Hale et al. (Unpublished manuscript, "Elevation-dependent symptom, mood, and performance changes produced by exposure to hypobaric hypoxia," B. Shukitt-Hale, L. E. Banderet, and H. R. Lieberman, 1996).

TIME COURSE OF EFFECTS

Because adverse changes in mood and cognitive performance occur at altitude, one interesting question is, What is the time course of these effects, and are they related to increases in the incidence of acute mountain sickness (AMS)? The number, severity, rapidity of onset, and duration of symptom, mood, and performance changes vary from person to person and are related to both level of altitude and rate of ascent (Hansen et al., 1967; Shukitt-Hale et al., 1991a). It is usually assumed that individuals afflicted with AMS will be more susceptible to changes in these other parameters. However, previous studies have suggested that their time courses are different (Banderet and Burse, 1991).



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